Seasonality of oxygen consumption in five common Antarctic benthic marine invertebrates

The waters of the Southern Ocean exhibit extreme seasonality in primary production, with marine life living below 0 °C for much of the year. The metabolic cold adaptation (MCA) hypothesis suggests that polar species need elevated basal metabolic rates to enable activity in such cold which should result in higher metabolic rates, or at least rates similar to temperate species. This study aimed to test whether any of the five common marine invertebrates around Adelaide Island (Western Antarctic Peninsula) displayed MCA: the suspension-feeding holothurian Heterocucumis steineni, the grazing limpet Nacella concinna, and the omnivorous brittle star, cushion star and sea-urchin Ophionotus victoriae, Odontaster validus and Sterechinus neumayeri, respectively. We also tested a second hypothesis that secondary consumers will exhibit less seasonal variation of metabolic rate than primary consumers. Routine oxygen consumption was measured in both the austral summer and winter using closed circuit respirometry techniques. Metabolic rates for all the species studied were low compared with temperate species, in a fashion consistent with expected temperature effects on biological systems and, therefore, the data do not support MCA. All the species studied showed significant seasonal differences for a standard mass animal except N. concinna. In two species N. concinna and H. steineni, size affected the seasonality of metabolism. There was no difference in seasonality of metabolism between primary and secondary consumers. Thus, for secondary consumers seasonal factors, most likely food availability and quality, vary enough to impact metabolic rates, and produce seasonal metabolic signals at all trophic levels. Other factors such as reproductive status that are linked to seasonal signals may also have contributed to the metabolic variation across trophic levels.